JAVA自定义注解（2）

这个例子在实际应用中是比较有用的，用来将配置文件（*.properties)或者系统属性中的指定属性名称的值加载进来。此例是和Spring结合使用的，所以其他配置就略过了。

1、定义注解@Property

package com.kute.test.selfannotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * 自定义注解@Property
 * 加载配置文件和相应的属性
 */

@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.TYPE, ElementType.METHOD })
public @interface Property {

    //属性名称
    String name() default "";
}

2、解析注解

package com.kute.test.selfannotation;

import java.lang.reflect.Method;
import java.util.Properties;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.beans.factory.config.PropertyPlaceholderConfigurer;
import org.springframework.util.ReflectionUtils;

public class PropertyParse extends PropertyPlaceholderConfigurer implements
        BeanPostProcessor, InitializingBean {

    private static Logger logger = LoggerFactory.getLogger(PropertyParse.class);
    private Properties pros = null;

    // 在spring容器实例化bean之后添加自己的逻辑
    public Object postProcessAfterInitialization(Object bean, String beanName)
            throws BeansException {
        return bean;
    }

    // 在spring容器实例化bean之前添加自己的逻辑
    public Object postProcessBeforeInitialization(Object bean, String beanName)
            throws BeansException {
        if (bean.getClass().getAnnotation(Property.class) != null) {
            Method[] methods = bean.getClass().getDeclaredMethods();
            for (Method method : methods) {
                Property p = method.getAnnotation(Property.class);
                if (p != null) {
                    //获得对应名称的属性的值
                    Object para = pros.getProperty(p.name());
                    //方法参数类型名称
                    String parameterName = (method.getParameterTypes()[0]).getName();

                    if (parameterName.equals("java.lang.Integer")) {
                        para = new Integer(para.toString());
                    }else if (parameterName.equals(
                            "java.lang.Double")) {
                        para = new Long(para.toString());
                    }else if (parameterName.equals(
                            "java.lang.String")) {
                        para = para.toString();
                    }
                    logger.info("获得了指定名称的属性的值：" + para);
                    ReflectionUtils.invokeMethod(method, bean,
                            new Object[] { para });
                }
            }
        }
        return bean;
    }

    // 在初始化bean的时候执行该方法
    public void afterPropertiesSet() throws Exception {
        //此方法的作用是将配置的和系统属性加载进来
        pros = mergeProperties();
    }

}

3、应用注解

package com.kute.test.selfannotation;

import java.io.Serializable;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

@Property
public class Teacher implements Serializable {

    private static final long serialVersionUID = 7651360997972750779L;
    private static Logger logger = LoggerFactory.getLogger(Teacher.class);

    @Property(name = "third.kute.blog")
    public void setValue(String value) {
        logger.info("成功设String值：" + value);
    }

    @Property(name = "second.kute.age")
    public void setValue(Integer value) {
        logger.info("成功设Integer值：" + value);
    }

    @Property(name = "first.kute.name")
    public void setValue(Double value) {
        logger.info("成功设Double值：" + value);
    }
}

4、配置文件（部分）（applicationContext.xml)

<!-- PropertyParse此bean是继承了PropertyPlaceholderConfigurer来加载配置文件 -->
    <bean class="com.kute.test.selfannotation.PropertyParse">
        <!-- 除了支持配置的*.properties外，还支持获取系统属性(System.getProperties() -->
        <property name="systemPropertiesModeName" value="SYSTEM_PROPERTIES_MODE_OVERRIDE" />
        <!-- 资源找不到不抛出异常 -->
        <property name="ignoreResourceNotFound" value="true" />
        <property name="locations">
            <list>
                <value>classpath*:/first.properties</value>
                <value>classpath*:/second.properties</value>
                <value>classpath*:/third.properties</value>
            </list>
        </property>
    </bean>

5、文件内容

first.properties

first.kute.name=36.0
first.kute.age=111111
first.kute.blog=http://blog.csdn.net/kutekute

second.properties

second.kute.name=37.0
second.kute.age=222222
second.kute.blog=http://blog.csdn.net/kutekute

third.properties

third.kute.name=38.0
third.kute.age=333333
third.kute.blog=http://blog.csdn.net/kutekute